.WMF Metafile Format

A metafile for the Microsoft Windows operating system consists of a collection of graphics device interface (GDI) functions that 
describe an image. Because metafiles take up less space and are more device-independent than bitmaps, they provide 
convenient storage for images that appear repeatedly in an application or need to be moved from one application to another. 
To generate a metafile, a Windows application creates a special device context that sends GDI commands to a file or memory for 
storage. The application can later play back the metafile and display the image. 
During playback, Windows breaks the metafile down into records and identifies each object with an index to a handle table. When 
a META_DELETEOBJECT record is encountered during playback, the associated object is deleted from the handle table. The 
entry is then reused by the next object that the metafile creates. To ensure compatibility, an application that explicitly manipulates 
records or builds its own metafile should manage the handle table in the same way. For more information on the format of the 
handle table, see the HANDLETABLE structure. 

In some cases, there are two variants of a metafile record, one representing the record created by Windows versions before 3.0 
and the second representing the record created by Windows versions 3.0 and later. Windows versions 3.0 and later play all 
metafile versions but store only 3.0 and later versions. Windows versions earlier than 3.0 do not play metafiles recorded by 
Windows versions 3.0 and later. 
A metafile consists of two parts: a header and a list of records. The header and records are described in the remainder of this 
topic. For a list of function-specific records, see Metafile Records. 

Metafile Header

The metafile header contains a description of the size of the metafile and the number of drawing objects it uses. The drawing 
objects can be pens, brushes, bitmaps, or fonts. 
The metafile header has the following form: 



typedef struct tagMETAHEADER {
    WORD  mtType;
    WORD  mtHeaderSize;
    WORD  mtVersion;
    DWORD mtSize;
    WORD  mtNoObjects;
    DWORD mtMaxRecord;
    WORD  mtNoParameters;
} METAHEADER;

Following are the members in the metafile header: 

mtType	Specifies whether the metafile is stored in memory or recorded in a file. This member has one of the 
following values: 

Value	Meaning

0	Metafile is in memory. 
1	Metafile is in a file. 

mtHeaderSize	Specifies the size, in words, of the metafile header. 
mtVersion	Specifies the Windows version number. The version number for Windows version 3.0 and later is 0x300. 
mtSize	Specifies the size, in words, of the file. 
mtNoObjects	Specifies the maximum number of objects that can exist in the metafile at the same time. 
mtMaxRecord	Specifies the size, in words, of the largest record in the metafile. 
mtNoParameters	Not used. 

Typical Metafile Record

The graphics device interface stores most of the GDI functions that an application can use to create metafiles in typical records. 
A typical metafile record has the following form: 



struct {
    DWORD rdSize;
    WORD  rdFunction;
    WORD  rdParm[];
}

Following are the members in a typical metafile record: 

rdSize	Specifies the size, in words, of the record. 
rdFunction	Specifies the function number. This value may be the number of any function in the table at the end of this section. 
rdParm	Identifies an array of words containing the function parameters (listed in the reverse order in which they are 
passed to the function). 

Following are the GDI functions found in typical records, along with their hexadecimal values: 

GDI function	Value

Arc	0x0817 
Chord	0x0830 
Ellipse	0x0418 
ExcludeClipRect	0x0415 
FloodFill	0x0419 
IntersectClipRect	0x0416 
LineTo	0x0213 
MoveTo	0x0214 
OffsetClipRgn	0x0220 
OffsetViewportOrg	0x0211 
OffsetWindowOrg	0x020F 
PatBlt	0x061D 
Pie	0x081A 
RealizePalette (3.0 and later)	0x0035 

Rectangle	0x041B 
ResizePalette (3.0 and later)	0x0139 
RestoreDC	0x0127 
RoundRect	0x061C 
SaveDC	0x001E 
ScaleViewportExt	0x0412 
ScaleWindowExt	0x0400 
SetBkColor	0x0201 
SetBkMode	0x0102 
SetMapMode	0x0103 
SetMapperFlags	0x0231 
SetPixel	0x041F 
SetPolyFillMode	0x0106 
SetROP2	0x0104 

SetStretchBltMode	0x0107 
SetTextAlign	0x012E 
SetTextCharacterExtra	0x0108 
SetTextColor	0x0209 
SetTextJustification	0x020A 
SetViewportExt	0x020E 
SetViewportOrg	0x020D 
SetWindowExt	0x020C 
SetWindowOrg	0x020B 

Placeable Windows Metafiles

A placeable Windows metafile is a standard Windows metafile that has an additional 22-byte header. The header contains 
information about the aspect ratio and original size of the metafile, permitting applications to display the metafile in its intended 
form. 
The header for a placeable Windows metafile has the following form: 



typedef struct {
    DWORD   key;
    HANDLE  hmf;
    RECT    bbox;
    WORD    inch;
    DWORD   reserved;
    WORD    checksum;
} METAFILEHEADER;

Following are the members of a placeable metafile header: 

key	Specifies the binary key that uniquely identifies this file type. This member must be set to 0x9AC6CDD7L. 
hmf	Unused; must be zero. 
bbox	Specifies the coordinates of the smallest rectangle that encloses the picture. The coordinates are in metafile units 
as defined by the inch member. 
inch	Specifies the number of metafile units to the inch. To avoid numeric overflow, this value should be less than 1440. 
Most applications use 576 or 1000. 
reserved	Unused; must be zero. 
checksum	Specifies the checksum. It is the sum (using the XOR operator) of the first 10 words of the header. 

The actual content of the Windows metafile immediately follows the header. The format for this content is identical to that for 
standard Windows metafiles. For some applications, a placeable Windows metafile must not exceed 64K. 

Note:	Placeable Windows metafiles are not compatible with the GetMetaFile function. Applications that intend to use the metafile 
functions to read and play placeable Windows metafiles must read the file by using an input function (such as _lread), strip 
the 22-byte header, and create a standard Windows metafile by using the remaining bytes and the SetMetaFileBits 
function. 

Guidelines for Windows Metafiles

To ensure that metafiles can be transported between different computers and applications, any application that creates a 
metafile should make sure the metafile is device-independent and sizable. 
The following guidelines ensure that every metafile can be accepted and manipulated by other applications: 

	Set a mapping mode as one of the first records. Many applications, including OLE applications, only accept metafiles that are 
in MM_ANISOTROPIC mode. 

	Call the SetWindowOrg and SetWindowExt functions. Do not call the SetViewportExt or SetViewportOrg functions if 
the user will be able to resize or change the dimensions of the object. 

	Use the MFCOMMENT printer escape to add comments to the metafile. 

	Rely primarily on the functions listed in Typical Metafile Record. Observe the following limitations on the functions you use: 

	Do not use functions that retrieve data (for example, GetActiveWindow or EnumFontFamilies). 

	Do not use any of the region functions (because they are device dependent). 

	Use StretchBlt or StretchDIB instead of BitBlt. 

Sample of Metafile Program Output

This section describes a sample program and the metafile that it creates. The sample program creates a small metafile that 
draws a purple rectangle with a green border and writes the words "Hello People" in the rectangle. 



MakeAMetaFile(hDC)
HDC hDC;
{
    HPEN     hMetaGreenPen;
    HBRUSH   hMetaVioletBrush;
    HDC      hDCMeta;
    HANDLE   hMeta;

    /* Create the metafile with output going to the disk. */

    hDCMeta = CreateMetaFile( (LPSTR) "sample.met");

    hMetaGreenPen = CreatePen(0, 0, (DWORD) 0x0000FF00);
    SelectObject(hDCMeta, hMetaGreenPen);

    hMetaVioletBrush = CreateSolidBrush((DWORD) 0x00FF00FF);
    SelectObject(hDCMeta, hMetaVioletBrush);

    Rectangle(hDCMeta, 0, 0, 150, 70);

    TextOut(hDCMeta, 10, 10, (LPSTR) "Hello People", 12);


    /* We are done with the metafile. */

    hMeta = CloseMetaFile(hDCMeta);

    /* Play the metafile that we just created. */

    PlayMetaFile(hDC, hMeta);
}

The resulting metafile, SAMPLE.MET, consists of a metafile header and six records. It has the following binary form: 



0001         mtType... disk metafile
0009         mtSize...
0300         mtVersion
0000 0036    mtSize
0002         mtNoObjects
0000 000C    mtMaxRecord
0000         mtNoParameters

0000 0008    rdSize
02FA         rdFunction (CreatePenIndirect function)
0000 0000 0000 0000 FF00  rdParm (LOGPEN structure defining pen)

0000 0004    rdSize
012D         rdFunction (SelectObject)
0000         rdParm (index to object #0... the above pen)

0000 0007    rdSize
02FC         rdFunction (CreateBrushIndirect)

0000 00FF 00FF 0000 rdParm (LOGBRUSH structure defining the brush)

0000 0004    rdSize
012D         rdFunction (SelectObject)
0001         rdParm (index to object #1... the brush)

0000 0007    rdSize
041B         rdFunction (Rectangle)
0046 0096 0000 0000 rdParm (parameters sent to Rectangle...
                    in reverse order)

0000 000C    rdSize
0521         rdFunction (TextOut)
rdParm
000C         count
string
48 65 6C 6C 6F 20 50 65 6F 70 6C 65   "Hello People"
000A             y-value

000A             x-value


